Mystery #3Tier 2the deep sea

Why is the bottom of the deep ocean pitch black and freezing cold?

Dive down through the sunlit blue and the water grows dimmer with every metre. Keep going and the blue fades to grey, then to total black, and the cold bites harder. At the very bottom it is darker than any night and near freezing. Why is the bottom of the deep ocean pitch black and freezing cold?

A deep-sea anglerfish with a glowing lure on a stalk above its head and a mouth full of long needle teeth, an animal that makes its own light where none arrives — Photo: public domain illustration · Public domain · via Wikimedia Commons

Your guess

What do you think runs out as you go deeper and deeper down?

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